This application pertains to the art of mixing or blending valves and fluid pressure regulators. The invention is particularly applicable to mixing valves for appliances which selectively mix hot and cold water and will be described with particular reference thereto. It will be appreciated, however, that the invention has other applications where pressure regulation and selectively controlled fluid mixing are desired, such as industrial formulating operations in which the flows of a plurality of liquid constituents are continuously mixed in preselected proportions, water temperature regulators in which hot and cold water are selectively mixed to maintain a constant water temperature, or the like.
Commonly, appliance mixing valves have directly controlled the flow of incoming hot and cold water with a hot water control valve and a cold water control valve. Note for example, U.S. Pat. No. 4,270,570, issued June 2, 1981 to L. A. Kolze and assigned to the assignee herein. Further, appliance mixing valves usually supplied hot, cold, or warm water at either a high or a low flow rate. To select the high or low flow rate, a flow rate control solenoid valve selectively connected the hot and cold solenoid valves with an unrestricted or high flow rate outlet and a restricted or low flow rate outlet.
One problem with the prior art mixing valves is that the flow rate from the mixing valve varied for hot, cold and warm water. The warm water being connected with two supply lines flowed at a faster rate than either the hot or the cold. Another problem was that variations in the hot and cold water line pressures not only varied the flow rates of hot and cold water but varied the temperature of warm water.
One solution was to use flow control washers in the hot and cold water inlets which generally equalized hot and cold water flow rates even with fluctuating line pressure and stabilized the temperature of the warm water. However, the flow rate of warm water through the mixing valve was still greater than the flow rate of hot or cold water. One problem with flow control washers was that they required precision manufacturing techniques and precise engineering tolerances. The durometer of the rubber and the diameter of the flow opening had to be carefully controlled. This required relatively expensive manufacturing techniques. Even with the expensive precision manufacturing techniques, the flow control flow rates tended to vary with temperature, particularly hot and cold water. The flow control properties of the washers varied, not only with temperature, but with age. With age the rubber hardened, particularly the rubber in the hot water flow path, changing the regulated flow rate.